Methods for forming a ruthenium-based film on a substrate

ABSTRACT

Methods for forming a film on a substrate in a semiconductor manufacturing process. A reaction chamber a substrate in the chamber are provided. A ruthenium based precursor, which includes ruthenium tetroxide dissolved in a mixture of at least two non-flammable fluorinated solvents, is provided and a ruthenium containing film is produced on the substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of Ser. No. 12/034,776, filedFeb. 21, 2008, now U.S. Pat. No. 7,906,175, issued on Mar. 15, 2011,which claims the benefit of US Provisional Application No. 60/890,916,filed Feb. 21, 2007, herein incorporated by reference in its entiretyfor all purposes.

BACKGROUND

1. Field of the Invention

This invention relates generally to the field of semiconductorfabrication. More specifically, the invention relates to a method offorming a ruthenium containing film on a substrate.

2. Background of the Invention

Ruthenium and ruthenium compounds such as ruthenium oxide are materialsconsidered to be promising for use as capacitor electrode materials inthe next generation DRAMs. High dielectric constant materials (akahigh-k materials) such as alumina, tantalum pentoxide, hafnium oxide,and barium-strontium titanate (BST) are currently used for thesecapacitor electrodes. These high-k materials, however, are producedusing temperatures as high as 600° C., which results in oxidation ofpolysilicon, silicon, and aluminum and causes a loss of capacitance.Both ruthenium and ruthenium oxide, on the other hand, exhibit a highoxidation resistance and high conductivity and are suitable forapplication as capacitor electrode materials. They also functioneffectively as oxygen diffusion barriers. Ruthenium has also beenproposed for the gate metal for lanthanide oxides. In addition,ruthenium is more easily etched by ozone and by a plasma using oxygenthan are platinum and other noble metal compounds. The use of rutheniumas a barrier layer separating low-k material from plated copper and as aseed layer has also been attracting attention recently.

High-quality films of ruthenium and ruthenium oxide (RuO₂) can bedeposited under appropriate conditions from a precursor of high-purityruthenium tetroxide (RuO₄). This precursor can also be used for thedeposition (film formation) of perovskite-type materials, such asstrontium ruthenium oxide, that exhibit an excellent conductivity and athree-dimensional structure very similar to that of barium-strontiumtitanate and strontium titanium oxide.

However, high-purity ruthenium tetroxide, is a strong oxidizing agent,and is considered to have a high toxicity. In addition, high-purityruthenium tetroxide has a boiling point of about 130° C. and thereforeit presents an explosion risk at high temperatures (above about 108°C.). It is therefore recommended that pure ruthenium tetroxide be storedat low temperatures in order to avoid its potential for decomposition(explosion).

Given these properties of ruthenium tetroxide (RuO₄) (particularly theexplosion risk during holding), when used as a reactant it is normallynecessary to use it diluted in an appropriate solvent. Water, carbontetrachloride, and alkanes, for example, are known for use as thissolvent.

In the case of water as a solvent it is further necessary to add astabilizer such as NalO₄ in order to prevent RuO₄ from reacting anddecomposing during holding. Further, the use of such an aqueous RuO₄solution as a ruthenium based precursor may result in the introductionof impurities into the film and the tool (e.g., reaction chamber).

The electronics industry is abandoning carbon tetrachloride due to itshigh toxicity; therefore it becomes a less than ideal solvent choice fora ruthenium tetroxide precursor solution.

Alkanes such as pentane and octane are can be used as solvents for RuO₄,but the reaction between the alkane (for example, pentane) and RuO₄causes the incorporation of carbon when alkane containing dissolved RuO₄is used as a ruthenium based precursor in film production. Carbon causesan increase in the resistance of ruthenium-type films, and as aconsequence the presence of carbon during film production can be seen asless than ideal.

BRIEF SUMMARY

Novel methods and formulations for providing a film on a substrate in asemiconductor manufacturing process are described herein. The disclosedmethods and formulations utilize a mixture of ruthenium tetroxidedissolved in a mixture of at least two non-flammable fluorinatedsolvents.

In an embodiment, a method for providing a film on substrate in asemiconductor manufacturing process comprises, providing a reactionchamber and a substrate contained within the chamber. A ruthenium basedprecursor is provided, where the precursor comprises a mixture of atleast two non-flammable fluorinated solvents, ruthenium tetroxidedissolved in the solvent mixture, and less than about 100 ppm ofmoisture. A ruthenium containing film is then deposited on thesubstrate.

Other embodiments of the current invention may include, withoutlimitation, one or more of the following features:

-   -   each of the non-flammable fluorinated solvents has the general        formula C_(x)H_(y)F_(z)O_(t)N_(u); wherein        -   x≧3        -   y+z≦2x+2;        -   z≧1;        -   t≧0;        -   u≧0; and        -   t+u≧0        -   wherein x, y, z, t, and u are all integers.    -   the solvent mixture is a mixture of methyl nonafluorobutyl ether        and ethyl nonafluorbutyl ether;    -   the solvent mixture comprises between about 10% and 90%,        preferably about 30%, by volume, of methyl nonafluorobutyl        ether;    -   the solvent mixture comprises between about 10% and 90%,        preferably about 70%, by volume, of ethyl nonafluorobutyl        either;    -   the precursor contains less than about 1 ppm of moisture;    -   the precursor contains less than about 1 ppm of unassociated, or        free, oxygen (O₂);    -   the pressure in the reaction chamber is maintained between about        0.01 torr and about 1000 torr;    -   the film is deposited onto a substrate which is maintained at a        temperature between about 50° C. and about 800° C., preferably        between about 100° C. and abut 600° C.;    -   a gaseous reducing agent is introduced into the reaction        chamber, and a ruthenium containing film is deposited on the        substrate through a reaction between the reducing agent and the        precursor;    -   the reducing agent is one of hydrogen, air or oxygen;    -   the reducing agent and the precursor are introduced into the        chamber simultaneously;    -   the precursor is introduced, in its liquid state, into a        vaporizer;    -   the precursor is at least partially vaporized to form a vapor        state precursor;    -   the liquid state precursor is introduced to the vaporizer        through a pressurization with an inert gas;    -   at least about 99% of the liquid state precursor is vaporized in        the vaporizer;    -   substantially all of the liquid state precursor is vaporized in        the vaporizer;    -   the liquid state precursor is vaporized at a temperature between        about 10° C. and about 80° C.;    -   the substrate is a silicon type substrate suitable for        semiconductor manufacturing; and    -   the substrate is a ceramic-based substrate.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter that form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand the specific embodiments disclosed may be readily utilized as abasis for modifying or designing other structures for carrying out thesame purposes of the present invention. It should also be realized bythose skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects for the presentinvention, reference should be made to the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich like elements are given the same or analogous reference numbersand wherein:

FIG. 1 illustrates one embodiment of an apparatus for depositing aruthenium containing film; and

FIG. 2 illustrates another embodiment of an apparatus for depositing aruthenium containing film.

DESCRIPTION OF PREFERRED EMBODIMENTS

Generally, the current invention relates to methods for providing a filmon substrate in a semiconductor manufacturing process comprises,providing a reaction chamber and a substrate contained within thechamber. A ruthenium based precursor mixture is provided, where theprecursor comprises a mixture of at least two non-flammable fluorinatedsolvents, ruthenium tetroxide dissolved in the solvent mixture, and lessthan about 100 ppm of moisture. A ruthenium containing film is thendeposited on the substrate.

Non-flammable solvents are preferably used in the precursor mixturebecause non-flammable solvents are preferred when the mixture is used inan environment above room temperature. Non-flammable solvents are alsopreferred because they generally minimize the risk of introducing carboninto the film deposited on the substrate. Generally, fluorinatedsolvents are preferred because the presence of fluorine in the solventmolecule makes it non-flammable, while introducing no appreciablenegative affect to the film composition.

In some embodiments of the current invention the solvent mixture is madeof at least two solvents, each of which can be described according tothe general formula:C_(x)H_(y)F_(z)O_(t)N_(u)

wherein:

x≧3;

y+z≦2x+2;

z≧1;

t≧0;

u≧0; and

t+u≧0, and

wherein x, y, z, t, and u are all integers.

Several solvents satisfy this general formula and would be suitable foruse in the solvent mixture. These solvents include: Methylperfluoropropyl ether; methyl nonafluorobutyl ether; ethylnonafluorbutyl ether;1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-(trifluoromethyl)-Pentane;3-ethoxy-1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2-trifluoromethyl-hexane;C₉F₁₂N; C₁₂F₂₇N; C₁₂F₃₃N; C₆F₁₄; C₈F₁₆; C₇F₁₆; C₅F₁₅H₂; C₄F₅H₅;1,1,2,3,3 penta fluoro propane; CF3CFHCF2CH2OCF2CFHOC3F7; andC3F7OCFHCF2CH(CH3)OCF2CFHOC4F9.

In one embodiment the solvent mixture is a mixture of methylnonafluorobutyl ether and ethyl nonafluorbutyl ether. Both of these areavailable commercially from the 3M Company, and are sold under the tradenames of Novec HFE 7100 and Novec HFE 7200. C₅F₁₀H₂ is also commerciallyavailable from DuPont under the trade name of Vertrel.

In some embodiments, the substrate on which the ruthenium containingfilm is deposited may vary. The substrate may be a semiconductorsubstrate which may have already had other layers of materials depositedupon it from other semiconductor manufacturing steps. The substrate mayalso be a ceramic substrate (e.g. silicon dioxide, etc), a metallicsubstrate, or a polymer substrate.

In some embodiments the substrate has a different shape. The substratemay be flat, such as a typical semiconductor wafer, or a ceramicsubstrate for hybrid circuits. The substrate may also be a bumped or aball shaped surface. The substrate may also be a nanoparticle or anothermaterial characterized by a large specific surface area.

The ruthenium tetroxide (RuO₄) concentration of the precursor mixtureaccording to the current invention is suitably selected as a function ofthe film formation conditions and the material of the substrate on whichthe film will be formed.

Embodiments of the ruthenium based precursor according to the inventionoffers at least the following advantages.

-   -   As RuO₄ in pure form poses an explosion risk, the dissolution of        RuO₄ in a fluorinated solvent mixture enables RuO₄ to be handled        in a stable form without risk of explosion during storage or        holding.    -   The non-flammable solvent mixture does not react with RuO₄ and        can therefore avoid the RuO₄ decomposition that occurs with the        use of water. This enables stable long-term holding (storage) of        the ruthenium based precursor.    -   The desired ruthenium-containing film can in fact be produced        since the non-flammable solvent fluorinated solvent in the        ruthenium based precursor does not react with RuO₄ when this        precursor is used in gaseous form to produce film by thermal        CVD.        -   In the case of the current ruthenium based precursor, the            non-flammable solvent mixture does not react with the active            Ru compounds produced when RuO₄ decomposes in the reaction            chamber and the solvent mixture is discharged from the            reaction chamber along with any unreacted gas. This makes it            possible to obtain the desired ruthenium-containing film            without it containing unwanted compounds such as oxides.        -   By contrast, if the ruthenium based precursor were formed by            dissolution of RuO₄ in water and then a film formation by            thermal CVD is carried out by delivering such a precursor in            gaseous form to a reaction chamber, the RuO₄ would undergo            decomposition and produce active Ru. This active Ru would            then react with the water, producing unwanted oxide. This            makes it difficult to produce the desired            ruthenium-containing film. In some embodiments, the            ruthenium based precursor is substantially free of moisture            content, containing less than 100 ppm, preferably less than            1 ppm of moisture.    -   The non-flammable solvent mixture in the ruthenium based        precursor is preferably not toxic. This makes it possible to        implement film production in a safe environment when a        ruthenium-containing film is produced by thermal CVD using the        gaseous ruthenium based precursor.    -   The fluorinated solvent mixture in the ruthenium based precursor        is preferably non flammable and exhibits a high thermal        stability, which makes it possible—when this ruthenium based        precursor is used in gaseous form for the production of        ruthenium-containing film by thermal CVD—to avoid incorporation        of carbon into the film as well as decomposition, combustion, or        explosion by the solvent mixture.

According to various embodiments, a ruthenium containing film is formedby depositing ruthenium containing film on a substrate by introducing,in gaseous form, at least the inventive ruthenium based precursor into areaction chamber that holds the substrate.

According to these methods, Ruthenium containing films that are possibleto deposit, include, but are not limited to:

-   -   a ruthenium film,    -   a ruthenium oxide film (RuO₂ film), and    -   a ruthenate film.        Method for Forming Ruthenium Film

According to an embodiment, a ruthenium film is formed by introducingthe ruthenium based precursor in gaseous form and gaseous reducing agentinto a reaction chamber that holds a substrate and depositing rutheniumon the substrate by reacting the precursor with the reducing agent.

In some embodiments, the ruthenium based precursor can be introducedinto the reaction chamber using a bubbler system. That is, the rutheniumbased precursor, being a liquid as noted above, may be held within avessel and an inert gas (e.g., nitrogen, argon, helium, etc.) may bebubbled into this (possibly temperature controlled) vessel using aninert gas bubbling tube, resulting in delivery into the reaction chamberof the inventive precursor entrained in the inert gas.

In some embodiments, the ruthenium based precursor may be introducedinto the reaction chamber through a direct vaporization system. Such asystem is known in the art, and may include a liquid mass flowcontroller and a vaporizer, such as a glass or metal tube. Inert gas(e.g. nitrogen, argon, helium, etc) may be used to pressurize the liquidphase ruthenium based precursor, and cause it to flow from its storagevessel, through a liquid flow controller, and into the vaporizer. Ifinert gas is not used to cause the liquid to flow, a vacuum (or lowerpressure condition) may be generated downstream of the precursor storagevessel, for instance, at the vaporizer outlet. In some embodiments, thevaporizer is heated to a temperature between about 10° C. and about 80°C. The temperature of the vaporizer causes the liquid phase precursor tovaporize into a vapor phase precursor. In some embodiments, about 99%,and preferably all, of the liquid phase precursor vaporize into a vaporphase precursor. This vapor phase precursor is then delivered to thereaction chamber.

In some embodiments, the reducing agent under consideration reducesruthenium tetroxide to ruthenium metal. This reducing agent can bespecifically exemplified by hydrogen (H₂), but is not limited thereto.

Other possible reducing agents include hydrazine and its derivatives andhydrocarbons (e.g. alkene, alkyne, aromatic rings, etc). A singlereducing agent or the combination of two or more reducing agents can beused. Hydrogen is particularly preferred for the reducing agent.

In some embodiments, either chemical vapor deposition (CVD) or atomiclayer deposition (ALD) can be used to form the ruthenium film.

In embodiments where CVD is the deposition method used, the gaseousreducing agent and gaseous ruthenium based precursor according to theinvention are introduced simultaneously in the reaction chamber. Thereducing agent and the RuO₄ in the precursor react in the gas phase,resulting in reduction of the RuO₄ to ruthenium, which deposits on thesubstrate. The non-flammable fluorinated solvent mixture thataccompanies the RuO₄ in the gaseous precursor does not undergodecomposition during this deposition, and its incorporation into theresulting ruthenium film is therefore also avoided.

The total pressure in the reaction chamber during this film productionis preferably maintained between about 0.01 torr to 1000 torr and ismore preferably maintained between about 0.1 torr to 10 torr. Thesubstrate is preferably heated to between about 50° C. to 800° C. and ismore preferably heated to between about 100° C. to 400° C. The reducingagent is admitted into the reaction chamber in sufficient quantity toreduce the RuO₄ in the precursor to ruthenium metal. When for examplehydrogen is used as the reducing agent, at least 4 moles hydrogen areused per 1 mole RuO₄ in the precursor. The by-product in this case isH₂O.

In some embodiments where ALD is the deposition method used, the gaseousruthenium based precursor is initially introduced into the reactionchamber and a very thin layer (e.g. a monoatomic layer) of rutheniumoxide is formed on the substrate by adsorption and decomposition of theprecursor. The interior of the reaction chamber is then purged with aninert gas (e.g. nitrogen, helium, argon) in order to remove theunreacted or unadsorbed ruthenium based precursor—which includes thehereinabove specified non-flammable fluorinated solvent mixture. Thispurge is followed by the introduction of the gaseous reducing agent intothe reaction chamber. The incoming reducing agent reacts with themonoatomic layer of ruthenium oxide formed on the substrate and reducesthe ruthenium oxide to ruthenium metal. This results in the formation ofa monoatomic layer of ruthenium on the substrate. When the growth of athicker ruthenium film is desired, the following sequence can berepeated after the unreacted reducing agent and gaseous reactionproducts generated by the reducing agent have been purged from thereaction chamber: introduction of the gaseous ruthenium based precursor,purge/removal of the residual ruthenium based precursor, introduction ofthe reducing agent, purge/removal of reducing agent and gaseous reactionproducts.

In some embodiments, the introduction of the gaseous ruthenium basedprecursor and reducing agent may be carried out by pulse delivery in thecase of ALD. The gaseous ruthenium based precursor can be introduced,for example, for between about 0.01 second to 10 seconds at a flow rateof about 0.1 sccm to 10 sccm and the reducing agent can be introduced,for example, for between about 0.01 second at a flow rate of about 0.5sccm to 100 sccm. The purge gas can also be introduced, for example, forbetween about 0.01 second to 10 seconds at a flow rate of about 100 sccmto 5000 sccm.

The total pressure in the reaction chamber during ALD may preferably bemaintained between about 0.1 torr to 10 torr, while the substratetemperature is preferably maintained at a temperature between about 100°C. to 600° C.

Method for Forming Ruthenium Oxide Film (RuO₂ Film)

According to some embodiments, the ruthenium based precursor isintroduced in gaseous form into a reaction chamber that holds asubstrate. This ruthenium based precursor can be introduced into thereaction chamber in gaseous form by a bubbler system or through a directvaporization system. In this case the substrate is heated to atemperature at which the RuO₄ in the precursor is decomposed and solidruthenium oxide (ruthenium dioxide) is produced. The solid rutheniumoxide produced by RuO₄ decomposition deposits on the substrate. Thenon-flammable fluorinated solvent mixture that accompanies the RuO₄ inthe gaseous precursor does not undergo decomposition during thisdeposition of ruthenium oxide, and its incorporation into the rutheniumoxide film is therefore also avoided. The solid ruthenium oxide (RuO₂)functions as a decomposition catalyst for the gaseous RuO₄. As a result,once the gaseous RuO₄ has been decomposed under the application of heatand solid ruthenium oxide produced by this decomposition has depositedon the substrate, the gaseous RuO₄ can be satisfactorily decomposed evenwhen the heating temperature is reduced.

The total pressure within the reaction chamber during this rutheniumoxide deposition is preferably between about 0.01 torr to 1000 torr andmore preferably is between about 0.1 to 5 torr. The substrate ispreferably heated to at least 150° C. and more preferably is heated to atemperature between about 350° C. to 400° C.

The substrate submitted to the film formation methods described abovecan be exemplified by semiconductor substrates such as siliconsubstrates. The following, for example, may be formed on thissemiconductor substrate: low-k film, high-k film, C-doped silicondioxide film, titanium nitride film, copper film, tantalum nitride film,molybdenum film, tungsten film, and ferroelectric film. The rutheniumfilms and ruthenium oxide films afforded by this invention exhibit anexcellent adherence to these films and will not debond even whensubmitted to chemical mechanical polishing (CMP). Moreover, theincorporation of impurities, such as carbon and halogens such asfluorine, is entirely absent from these ruthenium films, ruthenium oxideor ruthenium-containing films. In addition, an incubation period iseither unnecessary in the present invention or is very brief, whichenables deposition (growth) of the ruthenium films and ruthenium oxidefilms in a correspondingly shorter period of time (from the initialearly phase in the case of ALD, several minutes for CVD).

Turning now to FIG. 1, an illustrative example of an apparatus that maybe used to implement film deposition methods by CVD is described.

The apparatus illustrated in FIG. 1 is provided with a reaction chamber11, a feed source 12 for the ruthenium based precursor, a feed source 13for reducing agent gas, and a feed source 14 for an inert gas astypically used as a carrier gas and/or diluent gas. In the case of asingle-wafer tool, a susceptor (not shown) is provided in the reactionchamber 11 and a single semiconductor substrate (not shown), such as asilicon substrate, is mounted on the susceptor. The interior of thesusceptor is provided with a heater for heating the semiconductorsubstrate to the prescribed reaction temperature. In the case of a batchtool, from 5 to 200 semiconductor substrates are held in the reactionchamber 11. The heater in a batch tool may have a different structurefrom that of the heater in a single-wafer tool.

The feed source 12 for the ruthenium based precursor introduces theruthenium based precursor into the reaction chamber 11 using either thebubbler system or the direct vaporization system already described aboveand is connected to the inert gas feed source 14 by a line L1. The lineL1 is provided with a shutoff valve V1 and downstream therefrom with aflow rate controller, for example, a mass flow controller MFC1. Theruthenium based precursor is introduced into the reaction chamber 11from the feed source 12 through a line L2. The following are provided inthe line L2 considered from the upstream side: a UV spectrometer UVS, apressure gauge PG1, a shutoff valve V2, and a shutoff valve V3. The UVspectrometer UVS functions to confirm the presence and detect theconcentration of the precursor (particularly the RuO₄) in the line L2.

The feed source 13 for the reducing agent gas comprises a vessel thatholds the reducing agent in gaseous form. The reducing agent gas isadmitted into the reaction chamber 11 from this feed source 13 through aline L3. A shutoff valve V4 is provided in the line L3. The line L3 isconnected to the line L2.

The inert gas feed source 14 comprises a vessel that holds inert gas ingaseous form. Inert gas can be introduced from this feed source into thereaction chamber 11 through a line L4. The following are provided in theline L4 considered from the upstream side: a shutoff valve V6, a massflow controller MFC3, and a pressure gauge PG2. The line L4 joins withthe line L3 upstream from the shutoff valve V4. The line L1 branches offthe line L4 upstream from the shutoff valve V6.

A line L5 branches from the line L1 upstream from the shutoff valve V1.This line L5 joins into the line L2 between the shutoff valves V2 andV3. A shutoff valve V7 and a mass flow controller MFC4 are disposed inthe line L5 in the given sequence from the upstream side.

A line L6, which reaches to the reaction chamber 11, branches offbetween the shutoff valves V3 and V4. A shutoff valve V8 is provided inthis line L6.

A line L7, which reaches to a pump PMP, is provided at the bottom of thereaction chamber 11, and the following are provided in this line L7considered from the upstream side: a pressure gauge PG3, a butterflyvalve BV for adjusting the back pressure, and a hot trap 15. The hottrap 15 comprises a tube that is provided over its circumference with aheater. Since the RuO₄ in the gaseous precursor is converted into solidruthenium oxide by thermal decomposition, the RuO₄ introduced into thishot trap 15 can be eliminated from the gas stream by conversion intosolid ruthenium oxide, which deposits on the inner wall of the tube.

In order to produce ruthenium film using the apparatus illustrated inFIG. 1, the shutoff valves V1, V2, and V5 are first closed and theshutoff valves V6, V7, V3, V4, and V8 are opened. While operating thepump PMP, the inert gas from the inert gas feed source 14 are introducedinto the reaction chamber 11 through the line L4 and L5 via the line L6.

The shutoff valve V5 is then opened and reducing agent gas is introducedinto the reaction chamber 11 from the reducing agent gas feed source 13,followed immediately by the opening of shutoff valves V1 and V2 and theintroduction of inert gas from the inert gas feed source 14 through theline L1 and into the feed source 12 for the ruthenium based precursor.This results in the introduction of gaseous precursor (RuO₄ and thehereinabove specified non-flammable solvent, preferably a fluorinatedsolvent) into the reaction chamber 11 via the line L2 and the line L6.The reducing agent gas and RuO₄ react in the reaction chamber 11,resulting in the deposition of ruthenium metal on the semiconductorsubstrate.

In order to produce a solid ruthenium oxide film using the apparatusillustrated in FIG. 1, the apparatus is prepped by closing the shutoffvalves V5 as well as V4 and V6 and keeping these valves closed since thereducing agent gas will not be used. The pump PMP is started, a vacuumcondition is created, and shutoff valves V3, V7, and V8 are opened inorder to have inert gas flown in the reaction chamber. While in thisstate, the shutoff valves V1, V2, are opened and inert gas is introducedfrom the inert gas feed source 14 through the line L4 and the line L1into the feed source 12 for the ruthenium based precursor, resulting inthe introduction of gaseous precursor (RuO₄ and the hereinabovespecified non-flammable solvent, preferably a fluorinated solvent) intothe reaction chamber 11 via the line L2 and the line L6. Since thereaction chamber 11 is being heated, the RuO₄ introduced into thereaction chamber 11 undergoes thermal decomposition into solid rutheniumoxide, which deposits on the substrate.

Turning now to FIG. 2, an illustrative example of an apparatus that maybe used to implement film deposition methods by ALD is described.

The apparatus illustrated in FIG. 2 has a structure in which a line L8is provided in the apparatus illustrated in FIG. 1; this line L8 isitself provided with a shutoff valve V2′ and, downstream from theshutoff valve V2′, with a hot trap 15′ that is the same as the hot trap15. The same reference symbols have therefore been assigned to thoseelements that are the same as in FIG. 1, and these elements will not bedescribed in detail again. One end of the installed line L8 is connectedto the line L2 between the ultraviolet spectrometer UVS and the pressuregauge PG1, while the other end is connected to the line L7 between thehot trap 15 and the pump PMP.

In order to produce a ruthenium film by ALD using the apparatusillustrated in FIG. 2, the shutoff valves V2 and V5 are first closed andthe shutoff valves V6, V7, V3, V4, V8, and V9 are opened, as are theshutoff valves V1 and V2′. As the pump PMP is operating, a vacuum stateis generated in the different lines in which inert gas from the inertgas feed source 14 is introduced through the lines L4 and L5 and intothe reaction chamber 11 via the line L6. The passage of inert gasthrough the line L1, the feed source 12 for the ruthenium basedprecursor, results in the flow of gaseous precursor (RuO₄ and thenon-flammable fluorinated solvent mixture) in L2 and L8, along with theinert gas.

After this initial set up has been carried out, the shutoff valve V2′ isclosed and the shutoff valve V2 is opened and a pulse of gaseousprecursor is delivered into the reaction chamber 11. This is followed bythe simultaneous closure of the shutoff valve V2 and the opening of theshutoff valve V2′, which results in passage through the line L8 ofgaseous precursor along with inert gas which will be decomposed inhot-trap 15′. A purge of the reaction chamber interior by theintroduction into the reaction chamber 11 of inert gas from L4 and L5via L6 leading to the removal of unreacted precursor (including thesolvent mixture) and generated by-products from the interior of thereaction chamber 11. The shutoff valve V5 is then opened and a pulse ofreducing agent gas is delivered from the reducing agent gas feed source13 along with inert gas from the inert gas feed source 14 into thereaction chamber 11. This is followed by closure of the shutoff valveV5, resulting in the delivery of a pulse of inert gas into the reactionchamber 11 and removal of reaction by-products, unreacted reducingagent, etc., from the reaction chamber 11. This process cycle may berepeated until a ruthenium film with the desired thickness is obtained.Method for Forming Ruthenate Film

In some embodiments, a ruthenate film is formed by introducing thehereinabove specified ruthenium based precursor in gaseous form and agaseous organometallic compound into a reaction chamber that holds asubstrate and reacting the precursor and organometallic compound in thepresence of an oxygenated gas and thereby depositing ruthenate on thesurface of the substrate.

The ruthenium based precursor can be introduced into the reactionchamber by either a bubbler system or a direct vaporization system, asdescribed above.

When, for example, a ferroelectric film of BaRuO_(x) is to be produced,Ba(DPM)₂, which is a β-diketone/barium complex, can be used as theorganometallic compound. When a ferroelectric film of SrRuO_(x) is to beproduced, Sr(DPM)₂, which is a β-diketone/strontium complex, can be usedas the organometal compound. Here, DPM is an abbreviation fordipivaloylmethanate or 2,2,6,6-tetramethyl-3,5-heptanedionate (TMHD).

The oxygenated gas can be, for example, oxygen, ozone or N₂O.

In some embodiments, CVD may be used to form the ferroelectric filmsmentioned above, in which case the ruthenium based precursor in gaseousform and the organometallic metal in gaseous form are introduced intothe reaction chamber. The RuO₄ in the precursor and the organometalliccompound then react in the gas phase in the presence of oxygen,resulting, for example, in the formation of BaRuO_(x) (or SrRuO_(x)) andits deposition on the substrate. At the same time, however, thenon-flammable fluorinated solvent mixture, accompanying the RuO₄ in thegaseous precursor does not undergo decomposition during deposition ofthe ferroelectric film, thereby also avoiding incorporation into thefilm.

The temperature in the reaction chamber is preferably between about 450°C. to 800° C., which is the reaction temperature for these gases.

The ruthenate films (for example, BaRuO_(x) and SrRuO_(x)) produced bythis method exhibit ferroelectric properties and can be used, forexample, in capacitors. Moreover, since thin ferroelectric films can beproduced by this method, these films can be used as electrode materialsjust like the Ru films and RuO₂ films. In specific terms, theseferroelectric films (particularly SrRuO_(x)) can be used as the upperand lower electrode materials for a separate ferroelectric (or as abuffer layer between a ferroelectric and the electrode material). Theseferroelectric films, being oxides, can prevent oxygen and PbO diffusionwith respect to ferroelectrics such as lead lanthanate titanate (PLT)and lead zirconate titanate (PZT), and at the same time, by adopting thesame perovskite structure as these ferroelectrics, can increase theadherence at the interface of the electrode material with theseferroelectrics and can prevent or lessen, inter alia, generation of thelow dielectric constant layer that can occur at this interface and canprevent or lessen deterioration.

EXAMPLES

The following non-limiting example is provided to further illustrateembodiments of the invention. However, the examples are not intended tobe all inclusive and are not intended to limit the scope of theinventions described herein.

Example 1

Ruthenium precursors made of ruthenium tetroxide dissolved in a solventmixture of 48% HFE-7100 and 52% HFE-7200 were directly vaporized atvarious vaporizer temperatures to determine precursor liquid flow ratescorresponding to full direct vaporization (as defined as no liquidremaining in the vaporizer). High purity argon was used as carrier gasto pressurize the liquid precursor and cause it to flow into thevaporizer. The base vacuum pressure at the exit of the vaporizer was 67torr, and a glass U-tube filled with glass beads was used as thevaporizer.

Sample 1 2 3 4 [RuO₄] % 0.42% 1.5% 1.5% 1.5% Temp C. 50 50 30 30Pressure (torr) 67 67 67 67 Ar (sccm) 278 278 278 278 Precursor flow 1.81.6 1.8 1.6 rate (ml/min) Full Yes Yes Yes Yes Evaporization?

While embodiments of this invention have been shown and described,modifications thereof can be made by one skilled in the art withoutdeparting from the spirit or teaching of this invention. The embodimentsdescribed herein are exemplary only and not limiting. Many variationsand modifications of the composition and method are possible and withinthe scope of the invention. Accordingly the scope of protection is notlimited to the embodiments described herein, but is only limited by theclaims which follow, the scope of which shall include all equivalents ofthe subject matter of the claims.

What is claimed is:
 1. A composition comprising ruthenium tetroxidedissolved in a mixture of methyl nonafluorobutyl ether and ethylnonafluorobutyl ether.
 2. The composition of claim 1 having less thanabout 100 ppm of moisture.
 3. The composition of claim 1 wherein thesolvent mixture comprises between about 10% and 90% of methylnonafluorobutyl ether.
 4. The composition of claim 3 wherein the solventmixture comprises about 30% of methyl nonafluorobutyl ether.
 5. Thecomposition of claim 1 wherein the solvent mixture comprises betweenabout 10% and 90% of ethyl nonafluorobutyl ether.
 6. The composition ofclaim 5, wherein the solvent mixture comprises about 70% of ethylnonafluorobutyl ether.
 7. The composition of claim 6 further comprisingabout 30% methyl nonafluorobutyl ether.
 8. The composition of claim 7consisting essentially of ruthenium tetroxide dissolved in a solventmixture of about 70% of ethyl nonafluorobutyl ether and about 30% methylnonafluorobutyl ether.
 9. The composition of claim 7 consisting ofruthenium tetroxide dissolved in a solvent mixture of about 70% of ethylnonafluorobutyl ether and about 30% methyl nonafluorobutyl ether themixture having less than 100 ppm moisture.